It is desirable to test files at the point of manufacture, for example, in order to avoid the sale and delivery of files having characteristics which are unacceptable for their intended operation, or to test them subsequently at the point of use in order to determine if previously acceptable characteristics thereof have been retained over a period of time. Further, it is often desirable to retain an historical record of the characteristics of files for future reference as, for example, to compare a particular file's characteristics over time or to provide information for a statistical analysis of the characteristics of a large number of different files for future design reference purposes.
Test procedures have been described in the literature, as in "Federal Specification on File, Hand (American Pattern) and Rasp, Hand", published on Oct. 31, 1966, by the U.S. Government Services Agency, and identified by Document GGG-F-325b. Such test procedures basically involve checking a file manually on its tang hardness, hardness crack, warpage, and the uniformity of cutting. The performance of the file is determined using machine-cutting tests, as described therein. Additional acceptance testing criteria for American pattern files are also described in the government document FPNTP-A6-19428-A-8-22-72, published in 1972.
Key points relating to the above machine tests can be summarized as follows. The test bar is 1 inch square, AISI 4140 steel (uniformed hardened to Rc 35 .+-.2), and is "run-in" using a file of the same type, but not the file test samples, so that the surface of the test bar matches the contour of the test file. A load (i.e., a compressive force between the test bar and the file) is selected as 20, 25, or 30 pounds depending on the size, shape, and type of the file. A stroke rate of 50-65 strokes per minute with 51/2" of maximum stroke is used. The file lifts clear of the test bar on its return stroke. The purpose of the test is to obtain a measurement of the gram removal over 1000 or 2000 strokes and to calculate the average gram removal based on the test results of 12 sample files.
A later Federal Specification, identified as A-A-2312, was issued to supplement Document GGG-F-325 on Sep. 27, 1985 but discussed nothing new with respect to the machine-cutting tests portion of the previous documents, apparently because there exist so many shapes and sizes of files, that no easy common procedures have been devised to effectively describe the performance of so many different files.
During use in various applications, a file is expected to be sharp, to be able to remove material rapidly (often referred to as having a high cutting efficiency), and to last a relatively long time (i.e., to have high durability). Cutting efficiency is a function of the file's tooth design, construction, and pattern. Durability of a file is indicated by the total area it files throughout its working life and is an important factor since it determines the total work a file is capable of doing. Sharpness, indicated by well-shaped teeth, establishes the degree of effortlessness involved in performing a filing motion, i.e., ability to use the least amount of work to make a specified cut. Overall a file should be such that it can not only do more work in less time with less effort, but also it can do it better. The major concerns of most industrial file users are the "grams removal rate" (in effect, the cutting efficiency), which is defined as the total grams of material that can be filed away (removed) using a selected number of strokes, and total useful life of the file. In contrast many, if not most, domestic consumer users appear to be more concerned about the feeling of the file's sharpness during use.
It is desirable to provide better tool and testing procedures which significantly improve the ability to establish suitable and meaningful criteria for a file's operating characteristics, as well as to determine such characteristics for particular files for comparison with such criteria. Such tool and testing procedures would permit a more accurate prediction of the file's potential adequacy of performance during use so that files not satisfying such criteria can be suitably detected and the file either reworked or rejected before sale and delivery to a customer or so that the performance of files already in use can be periodically rechecked.